# UART ESD protection, and is it necessary on inter-board connections?

This is probably a straightforward question, but I wanted to ask just to be on the safe side. I have a Wifi Module that I'm connecting to an ARM Cortex M4 uC, and it interfaces via UART.

Since I tend to throw on ESD and EMI protection on any lines communicating with the outside world, I figured I would add it to the UART lines. Typically, though, the two UART lines, TXD and RXD are purely inter-board - meaning that the only connection is between the module and the uC. In this case, I typically forgo the rigorous ESD protection and simply use a series resistor.

However, I've also added headers on these lines so I can use a logic analyzer and an FTDI chip for programming. This being the case, should I add additional ESD protection? Or could I add switches to disconnect the lines from the uC while programming the module?

If I should add extra protection, could anyone suggest any devices to do so? I've used a few ICs for SD Card interfaces and USB lines, but I have yet to come across one for UART.

Any input is appreciated.

• The same ICs you already use should work fine for a USART. – Ignacio Vazquez-Abrams May 13 '15 at 22:58
• @IgnacioVazquez-Abrams That's good to know. Thanks. – Mlagma May 13 '15 at 23:01
• Maybe some reference to specific parts could make this question more useful for the community. Feel free to answer to your own question, if @IgnacioVazquez-Abrams doesn't want to add a complete answer. At least you should edit your question describing what parts you use for protection. – Lorenzo Donati -- Codidact.org May 13 '15 at 23:58
• @LorenzoDonati I'll add an answer once I finish the schematic detailing the portion of my circuit I posted about. – Mlagma May 14 '15 at 3:14
• I'd say it depends on whether the UART is logic-level or RS-232 level. Simply because logic-level is dealing with chip inputs as opposed to RS232, which is ruggedized for very long cabling runs. Yet, if the chips are bipolar instead of MOS as @Dean explains, it will matter far less. Bottom line is, the chips in question very likely have protection diodes on their pins anyways, and would be "safe" for most human-body-model ESD. This may be one of those scenarios where, if you were that concerned, you actually make a test rig, charge up a probe and zap a pin, then record the result. – rdtsc Dec 28 '15 at 15:33